1. Field of the Invention
The present invention relates to an improvement of a control apparatus for a drive system of a hybrid vehicle.
2. Description of Related Art
There is known a hybrid vehicle drive system including: a first differential mechanism provided with a rotary element connected to an engine and a rotary element connected to a first electric motor; a second differential mechanism provided with a rotary element connected to a second electric motor and a rotary element connected to an output rotary member; a first clutch configured to selectively connect the rotary element of the first differential mechanism connected to the engine, to the rotary elements of the second differential mechanism; a manually operated shifting device; and a parking lock mechanism provided with a parking lock gear which is fixed directly or indirectly to the output rotary member and a rotary motion of which is prevented when the shifting device is placed in a parking position. Regarding this hybrid vehicle drive system, there has been proposed a technique for reducing an impact torque transmitted to a rotor of the second electric motor when the parking lock mechanism is operated to release the parking lock gear. Patent Documents 1 and 2 disclose examples of a control apparatus for such a hybrid vehicle drive system.
According to the prior art technique described above, the impact torque is reduced by placing a brake in a slipping state when the parking lock mechanism is operated to release the parking lock gear. However, this prior art technique does not necessarily permit sufficient reduction of the impact torque transmitted to the second electric motor upon releasing of the parking lock gear, since an inertia of the second electric motor is comparatively large. A comparatively large impact torque applied to the second electric motor may deteriorate durability of the hybrid vehicle drive system. In view of this drawback, there has been a need for development of a control apparatus for a hybrid vehicle drive system, which control apparatus permits effective reduction of deterioration of durability of the hybrid vehicle drive system due to the impact torque generated upon releasing of the parking lock gear.